Carburetor



May 4 1965 M. c. BROWN ETAL 3:18-1:843

GARBURETOR Filed Dec. 17, 1962 E /3 60 2 /8 la 4,

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A INVENToRs MORRIS C. BROWN United States Patent VOffice 3,181,843 Patented May 4, 1965 3,181,843 CARBURETOR Morris C. Brown, St. Louis, and Eldon A. Johnson, Sunset Hills, Mo., assignors to ACF Industries Incorporated, New York, N.Y., a corporation of New Jersey Filed Dec. 17, 1962, Ser. No. 245,172 3 Claims. (Cl. 261-67) This invention is directed to a carburetor and particularly to a carburetor of the type having a fuel chamber with one wall formed by a flexible movable diaphragm for controlling inlet valve to the fuel chamber.

Manually operated power tools utilize an internal combustion engine having a small diaphragm operated carburetor to operate in any position. [For this purpose such carburetors utilize a closed fuel chamber instead of a fuel bowl. The fuel chamber is one having a movable wall formed by .a diaphragm sealed across the cham-ber. The fuel inlet passage to the fuel chamber is controlled by an inlet valve operatively connected -to the movable portion of the diaphnagm. The diaphragm itself is moved to operate the inlet valve by the differential in pressure between the Ifuel pressure within the chamber and air pressure on the other side of the diaphragm outside of the fuel chamber. The yair pressure is provided by a dir-ect connection to the atmosphere or may be provided by a connection to the air horn of the carburetor. lDuring engine operation, the .air pressure on the outside of the diaphragm -is normally of a greater value than the pressure of fuel within the fuel chamber so that the diaphragm is moved inwardly by the pressure to open the inlet valve and permit fuel flow through the carburetor .to the engine.

lCarburetors of this type normally have -two fuel systems. One fuel system provides the optimum air and fuel mixture to the engine when the throttle is closed and the engine is operating at low speeds under no load. The other main or primary fuel system provides an optimum fuel and -air mixture to the engine when the throttle is opened to .any posit-ion from closed to a full open position, for varying load conditions. One particularprob- Ilem which is chronic with carburetors of 4this type is the transition from one fuel system to the other. Whe-n the engine is operating at low speeds with .a closed throttle, .a minimum .amount of fuel and air passes through the carburetor to the engine for its low speed operation. The high speed operation of the engine does not function until the throttle is opened and a sufficient flow of air through the carburetor induces a low pressure in the venturi or restricted region of the mixture conduit to suck fuel through the main fuel system.

One problem in carburetors of this type is the tendency of the engine to falter or stumble due to lack of sufficient fuel because of the delay of the main fuel system going into .action upon opening of the throttle. This is an inherent weakness and many solutions of the problem have been presented. One form of structure to provide suicient fuel during the change-over to the main fuel system from the low speed system is the provision of an accelerating pump which operates upon opening of the throttle by .a mechanical linkage between the pump and throttle. As the throttle is opened the pump exerts pressure on a supply of fuel to force it into the mixture passage and thus prov-ide sufficient fuel during the changeover period from low `speed to high speed operation.

In `carburetors of the type describ-ed utilizing a diaphragm fuel operated fuel chamber control, it is a desirability to retain the carburetor structure as sim-ple and to a minimum number of parts. It is thus an object of this invention to provide a means for forcing accelerating fuel into the mixture conduit as the throttle is opened to change from low speed to high speed operation of the engine to prevent stalling or stumbling of the engine.

It is an additional purpose of this invention to provide -a simple means for forcing an :additional supply of fuel to the carburetor ,and engine, while the engine is going from low speed to high speed operation upon theopening of the throttle. Y

The invention involves the use of the control diaphragm in the fuel chambre-r to force yan accelerating amount of 'fue-l into the mixture conduit of the carburetor upon opening of the throttle. This is done by increasing the controlling air pressure on the -outside of the diaphragm with the rapid opening of the throttle valve so that the Idiaphragm will be pressed inwardly to force additional fuel through the fue-l passages into the mixtu-re conduit. This sudden `increase in control yair pressure on the diaphragm is provided by connecting the air chamber to the inanifold or crankcase of -the internal combustion engine, so that upon opening of the throttle, particularly when the throttle is opened rapidly, the quick change in manifold or crankcase pressure is reflected in the control chamber of the fuel reservoir and a burst of fuel is injected into the mixture conduit to provide a suicient amount of fuel to prevent stumbling or stalling lof the engine.

'FIGURE 1 is a longitudinal sectional view of a carburetor in 4accordance with the invention connected to ,an engine.

lFIGURE 2 is a sectional view laterally of the carburetor structure of FIGURE l.

FIGURE 3 is Ia partial sectional View of a portion of the carburetor of FIGURES 1 and 2 showing a por-tion of the low speed circuit of the carburetor.

FIGURE 1 shows .a carburetor 10 in accordance with the invention connected to an engine E partially shown in the figure. The carburetor 16 Iconsists substantially of 5a tubular member I1:1 having a longitud-inal passageway 12 extending through .a flange 13 rand in alignment wi-th anopening=14 into the engine E. The opening 114 may be ian opening into the intake manifold of a four cycle engine or into the engine crankcase of a two cycle engine. At the other end of the passage `12 from the engine there -is mounted an air filter d6 consisting of a sheet metal annular housing filled lwith an air filtering material 118 which may consist of a type of liber matting or synthetic plastic foam material through which air may readily pass.

Mounted within the tubular mixture passage is a throttle valve 20 of a circular configuration, which tits across the passage 12 when Vin its closed position shown in FIGURE 1. To rotate the throttle 20 between an open and a closed position the throttle is mounted on a shaft 22 journaled in the wall of the tubular conduit 12 and having one end. 24 extending outwardly of the carburetor to which is attached an operating lever 26 for throttle operation.v

movement on a choke shaft 29 journaled in the wall of conduit 12. Manual means are also provided for opening and closing the choke valve 28 when desired. This manual means is not shown in the figures but may be of any well known and conventional structure. Between the choke shaft 29 and the throttle shaft 22, the mixture conduit 12 has a restricted portion formed with a venturi surface 30 which provides a throat or constriction of the conduit 12 and which is also provided with a flaring skirt portion 32 between the venturi surface 30 and the downstream end of the conduit 12.

A fuel chamber 34 is provided below the mixture conduit 12, as viewed in FIGURES 1 and 2. The fuel chamber is formed between a recess 35 in the body 11 of the carburetor and a flexible diaphragm 36 stretched across the recess 35 and sealed around its periphery by the rim of a cap structure 38 fixed to the carburetor body by machine screws 48, as indicated. A fiber washer 42 is fitted between the rim of cap 38 and the periphery of the diaphragm 36. To the center of the diaphragm 36 are fixed a pair of backing plates 44 which are fastened together with the diaphragm inbetween by a rivet 46. Between the diaphragm assembly and the cap 38 is an air chamber 48 to provide control of the diaphragm 36.

Fuel is delivered into the fuel chamber 34 from a fuel tank or reservoir 50 schematically indicated in FIGURE 2 through an inlet line 52 connected to one end of an inlet fitting 54. The other end of fitting 54 joins at one end to an inlet fuel chamber 56 of a fuel pumping structure closed by an inlet valve 58. A pumping chamber 68 is separated from a pulsation chamber 62 by a pump diaphragxn 64. The pulsation chamber 62 is connected by an air passage 66, shown in dotted lines in FIGURE 1, to the intake manifold or crankcase of the engine E through the opening 14. During engine operation, pulsations within the crankcase or manifold are transmitted through passage 66 to the chamber 62 for operating the pump diaphragm 64. Fuel is thus drawn into the pump chamber 68 and then out through an outlet check valve 68 into connected passages 70 and 72. A portion of fuel passage 72 is controlled by a needle inlet valve 74 having a pointed end operating against a resilient seat 76 to control the flow of fuel from the pumping chamber 60 into the fuel chamber 34. The inlet valve 74 is Operated in a closed direction by a coil spring 78 axially mounted around the valve 74 and pressing the pointed end of the valve onto the seat 76. rl`he spring 78 is mounted between a flanged end of the valve 74, as shown in FIG- URE 2, and a portion of a fitting 80 enclosing the valve 74. The lower end of the valve 74 is formed with a nail head 82 into which a bifurcated end of a lever 84 is fitted. The lever 84 is fulcrumed on a pin 85 mounted within the body cavity 35. The other end of lever 84 rests against the rivet 46 of the diaphragm assembly.

The high speed circuit of the carburetor consists of a recess 86 extending from the fuel chamber 34 into the body 11 of the carburetor to a cross passage 90, in which is threaded an adjustment needle 92. Needle 92 has a tapered end 94 extending into a restricted passage 95 between the bore 90 and a fuel well 96 drilled into the body 11. Restricted passage 95 may have an inside diameter of 0.052 inch. A plastic tubular fitting 98 is pressed into a stepped bore 97 and has a flanged end for separating fuel well 96 from fuel chamber 34. Fitting 98 is spaced from the wall of well 96 and has ports through the side walls connecting well 96 to the interior of fitting 98. A tubular nozzle structure 109 is fitted through the upper end of fitting 98. The free end of the tubular nozzle 188 extends through the Venturi surface 30.

A low speed circuit of the carburetor is shown specifically in FGURES 1 and 2 and consists of a recess 102 connecting the fuel chamber 34 with a cross passage 104 in which is threaded a low speed control needle 106. In a manner similar to the control needle 92, needle 106 has a tapered end 198 extending into a restricted passage 4 110 connecting the cross passage 104 with a low speed fuel well 112. Well 112 is separated from the fuel chamber 34 by a press-fitted disk 114. As shown in FIGURE 1, an idle port 116 extends from the low speed fuel well 112 into the mixture passage 12 downstream of the throttle 20 in its closed position, as shown in FIGURE 1. Idle air ports 118 and 119 connect the idle fuel chamber 112 with the mixture conduit upstream of the closed position of throttle 20.

An air passage 124 extends from the air control chamber 48 in cap 38 through the cap 38 and a portion of the carburetor body 11 and joins with a cross passage 126 extending from a small restriction 129 through the flange 13 of the carburetor to a point adjacent to the fuel well 96. Passage 126 connects at its inner end with a downwardly directed cross passage 128 which intersects a second cross passage 130 extending therefrom to the air horn 27 and substantially parallel to the mixture conduit 12. The air horn end of passage 130 is closed and a port 132 is formed through the side wall of the air horn 27 upstream of the closed position of choke valve 28 into the adjacent end of the passage 130. The downwardly directed passage 128 opens to a port 133 into the mixture conduit 12 and in the flaring skirt portion 32. A

In operation, turning over the engine E with throttle 20 open and choke 28 closed provides a vacuum or low pressure within the manifold or crankcase 14, which extends with the carburetor conduit 12. The low pressure or manifold vacuum downstream of the closed choke 28 will extend into the nozzle 100 and is transmitted through the fuel passages to the fuel chamber 34. The air pressure in conduit 12 upstream of the closed choke 28 is substantially atmospheric and is transmitted through passages 130, 128, 126 and 124 to the air chamber 48. This air pressure against the underside of the diaphragm 36, as viewed in FIGURES 1 and 2, will press the diaphragm upwardly and open valve 74. Engine pulsation through air passage 66 will operate the pump diaphragm to bring fuel into the carburetor and force it into fuel chamber 34, through recess 86 and passage 90 into the fuel well 96 through the nozzle 100. Fuel will also flow through the low speed system through recess 102, passage 104 into the idle well 112 and out the idle ports 116 and 118. Air sucked through the choke valve 28 into the mixture passage 21 will mix with this fuel to provide an enriched starting air and fuel mixture for the engine.

After the engine starts, the choke valve 28 is opened and for low speed operation, the engine is allowed to operate with the throttle in the closed position, shown in FIGURE 1. The area in the mixture passage in the region of the venturi 30 is now substantially at atmospheric pressure and with no pressure differential between the end of nozzle 100 and fuel chamber 34, no fuel is urged through the nozzle 100. However, low pressure inthe mixture passage 12 downstream of the closed throttle 20 will continue to pull fuel out of the idle port 116. Idle air will flow through the ports 118 and 119 into the idle well 112 to mix with this fuel to provide a sufficient air and fuel mixture for low speed operation of the engine. The optimum amount of fuel flow out of the port 116 is obtained by the adjustment of needle 166.

Upon opening of the throttle 20 to -a full open position, air will flow rapidly through the mixture passage in response to the engine. At the venturi restriction 38, the air flow will provide a low pressure region so that fuel will be urged out of the nozzle 100 by air pressure in chamber 48 on the diaphragm 36. The amount of fuel for optimum high speed engine operation is obtained by the adjustment of the high speed needle 92.

During operation of the engine, the subatmospheric conditions in the region of the venturi 30 or at the idle port 116 are reflected in the fuel well 34, which keep the fuel in chamber 34 at a subatmospheric pressure. This results in a higher air pressure on the lower side of the diaphragm 36 pressing the diaphragm inwardly against the bias of spring 78 to rotate the lever S4 in a clockwise direction, as viewed in FIGURE 2, the holding valve 74 open. During low speed operation, since the flow of fuel out of the idle port 116 is relatively small, the opening of the valve 74 is to a much less degree than during high speed Ioperation of the engine when a greater amount of fuel liows through the main nozzle 100. During operation of the engine then, the diaphragm and needle assembly occupy substantially static or equilibrium position at which the fuel ow past the valve 74 into the fuel chamber 34 equals the flow of fuel out of the chamber 34 into either the high speed circuit or the low speed circuit of the carburetor.

The pressure of the air in chamber 48 is determined by the air pressure at port 132 in the air horn connecting passage 130 to the air horn and at port 133 connecting passage 128 to the venturi skirt. Port 132 is always substantially at a pressure a little lower than atmospheric, due to the resistance set up by the air `filter 18, while the air pressure during engine operation at port 133, in both the two cycle and four cycle engines is also substantially at atmospheric pressure during idle conditions when the throttle is closed. However, as the throttle 20 is opened in the operation of either type of engine, the pressure in the venturi skirt 32 falls slightly below atmospheric pressure toward a negative pressure of approximately two inches of mercury at wide open throttle. The purpose of utilizing the two ports 132 and 133 to determine the pressure of air in chamber 48 is to slightly lower the pressure in the chamber during Wide open throttle or high speed conditions, which will result in a slightly lower position of the diaphragm, as viewed in FIGURES l and 2, with a slight closing of the inlet needle 74 to lean out the fuel mixture at high speeds. However, during any degree of engine oper-ation, the ports 132 and 133, either alone or in combination, will always provide within the chamber 48 an air pressure greater than the pressure of the fuel in chamber 34 which is determined by the drop in pressure at the idle port 116 or at the main fuel nozzle 188. This is necessmy so that the air pressure in chamber 48 will be able to overcome the force of spring 78 to open inlet valve 74 during engine operation.

In passage 130 a restriction 135 is provided to limit the air passing into the passage 130 from port 132 to a predetermined amount. Furthermore, within the passage 128 a restriction 137 is provided to also limit the ilow of air through the passage 128. It is obvious that when the ports 132 and 133 are substantially at the same pressure because of the closed throttle 2i), there is no ow of air between the ports. However, during high speed operation, when the throttle is moved towards a wide open position and a depression results at the port 133 there will be a slight flow of air through the port 132 at a higher air pressure through the passage 130 and out the port 133. This iiow of air will cause a drop in pressure in the air passage 130 because of the restriction 135. This drop in pressure in passage 130 is reflected through passages 128 and 124 into the air chamber 48. This results then, as set forth above, in the pressure in chamber 48 being at a slightly lower pressure than would exist, if there was no port 133.

In accordance with the invention, a second control air passage 126 connects the chamber 48 through passage 124 to the manifold or crankcase of the engine and adjacent to the opening 14. The purpose of the control passage 126 is to provide a means for detecting in the air chamber 48 changes in pressure in crankcase or manifold so that an acceleration effect can be provided upon sudden opening of the throttle.

At wide open throttle, the air in passage 126 which is connected by passage 127 to the crankcase or manifold of the engine E, is at a pressure a little below atmospheric pressure, so that there is little or no flow through passages 126 and 127 which would change or alter the controlling 75 pressure in chamber 48. However, during idle conditions of engine operation with closed throttle with a two cycle installation, when passage 127 is connected to the crankcase of the engine, the pressure within the crankcase may be anywhere in the range of a negative 28 inches of water to a negative 40 inches of water pressure. In a four cycle installation during idle or low speed operation with closed throttle, passage 127 connects to the intake manifold of the engine and the pressure in the manifold is between a negative 10 inches to a negative 20 inches of mercury pressure. Thus, in going from closed throttle conditions to a wide open throttle condition, the air pressure would in either the crankcase of a two-cycle engine or the manifold of a four cycle engine undergo a considerable change.

It is desirable in carburetors of this typewhich may be operated by a single manual trigger to be able to go quickly from low speed operation at closed throttle to a high speed operation at wide open throttle with the provision of suicient fuel to prevent stalling or stumbling of the engine. Oftentimes during low speed operation the fuel level in nozzle tends to drop and considerable air is drawn through nozzle 100 into the nozzle chamber 96. Then, when the throttle 20 is suddenly opened and a suction is created yat the end of nozzle 160 because of the venturi effect there is no fuel immediately available due to the presence of air in the nozzle chamber. Because of this, the engine may stumble and even stall out. However, with the sudden opening of a throttle 28, the pressure in the crankcase or manifold of the engine instantaneously rises from the low negative pressures set forth above to substantially atmospheric pressure. Since, in accordance with the invention, the control chamber 4S is connected through passages 126 and 12.7 to the crankcase or manifold of the engine, this instantaneous increase in pressure is felt within the chamber 48 in the form of a pulse which will provide a sudden increase in pressure in chamber 48 and press the diaphragm upwardly, .as viewedin FlG- URES l and 2. This pressure upwardly on the diaphragm forces fuel quickly through the main fuel passages S6, 95 and through the nozzle chamber 96 and the nozzle 18) so as to force the fuel out the nozzle immediately after the opening of the throttle to a wide open position. IIhis provides suflicient fuel to mix with t-he sudden increase of air rushing to the engine by the opening of the throttle, and forms a rich air and fuel mixture for instant acceleration of the engine.

The restriction 129 is provided in the passage 126 to limit the how of air from passage 126 into passage 127 and the engine crankcase or manifold when the engine is operated `at low speed with the throttle closed. This restriction must be very small and of a size to prevent the lowering of the pressure in the chamber 48 to an inoperable value, at which the pressure in the chamber is unable to control the diaphragm and open the needle 74. In fact, the size of the restriction 129 must be only suftcient to slightly drop the pressure in chamber 48 and yet retain suiiicient pressure within the chamber to operate the diaphragm in the manner described above. However, the size of the restriction 12.9 must also be large enough to allow an instantaneous change in pressure in the air chamber 48 in response to the change in engine, manifold or crankcase pressure upon the sudden opening of the throttle. Because of the restrictions and 137 in passages 138 and 128,7rcspectively, the pulse of air passing through restriction 129 is directed fully into the chamber 48 through the passage 124.

Also in accordance with the invention, Va metering needle 148 is fixed at its lower end, as viewed in FIG- URES 1 and 2, into the rivet structure 46. The upper end of the metering needle 148 passes through a centrally formed aperture 141 through the base of the tubular fitting 98. The upper portion of the needle has an-outside diameter of substantially the same size as the inner diameter of the aperture 141, so that, when the upper portion aislada of the metering rod 149 is within aperture 141, substantially no fuel flows through aperture 141 into the interior of the fitting 98 from the fuel chamber 34. Between the upper portion of the rod 14d and the portion gripped by the rivet 46, the metering rod is tapered at 142, as shown in FIGURES l and 2, so that as the diaphragm rises under pressure in chamber 48, the tapered portion 142 enters the aperture 141 and permits fuel to iiow directly from the chamber 34 into the fitting 98 and out the nozzle 100. As viewed in FIGURES l and 2, the position of the diaphragm 36 is illustrated as that which the diaphragm would have during the low speed or idle operation of the engine at closed throttle. As seen in FIGURE 2, the inlet needle 74 is slightly displaced from the seat 76 so that fuel may flow from the passage 72 into the fuel chamber 34 to take care of the low speed conditions of the engine. As seen in FIGURE 1, during this low speed operation of the engine, the upper portion of the metering rod 149 is within the aperture of fitting 98 and prevents fuel Jlow into the fitting 98 directly. However, as the throttle is opened, because of a pressure drop in the region of venturi 30, the fuel pressure within chamber 34 drops slightly below that which it has during low speed operation of the engine and air pressure in chamber 48 forces the diaphragm upwardly to a higher level, as described above. At this level the inlet valve 74 is opened to permit a greater flow of fuel into and through the fuel chamber T14. Also, as the diaphragm is raised to the higher level, the upper portion of the tapered end 142 of the metering rod 14) enters within the aperture of fitting 95 and permits fuel to ow directly into the fitting g3 and through the nozzle 100 from the fuel chamber 34. During the rapid acceleration from low speed to high speed, described above, when the throttle valve 2) is suddenly opened and the air pulse through passages 127 and 125 forces the diaphragm, for an instant, to a higher position, more of the tapered portion 142 of the metering rod 14h enters the aperture of fitting 98 so the sudden increase in pressure within the fuel chamber caused by the diaphragm will force fuel not only through the main passages, as described, but also directly through the central aperture of the fitting 93 to permit thus a direct flow from the fuel chamber and out the nozzle 100 for rapid acceleration.

When the engine is shut off, the various pressures within the chambers 34 and 48 return to substantially atmospheric and the spring 78 forces the needle 74 to its closed position. The lever 84 returns the diaphragm to its lowest position below the position it assumes during low speed or idle operation of the engine and pulls the top of the upper end of metering rod 140 into the aperture 141 of the fitting 98. Because of the close fitting between the i rod and the aperture 141, fuel iiow through aperture 141 is closed off. As described above, the tapered portion 142 is within aperture 141 during any open position of throttle 2t). The taper of rod portion 142 is formed so that most of the fuel needed by the engine during any open position of the throttle passes through aperature 141 and the adjustment needle 92 provides an adjustment of the balance of the fuel required. This results in the relative adjustment of needle 92 being less critical and also permits the needle end 94 to be only slightly spaced from passage 95 so that fuel will be held between them by a capillary effect during all speeds of engine operation. As described above, the upper end of rod 14) closes aperture 141 with a close lit, during low speed operation of the engine, which is also sealed by the capillary effect of the fuel between rod 140 and aperture 141. Thus, at close throttle operation of the engine the passages 95 and 141 between the nozzle and fuel chamber 34 are sealed by fuel which prevents any bleeding of air through nozzle 1u@ into chamber 34 because of the pressure differential between the air conduit 12 upstream of the closed throttle and the fuel chamber 34.

As shown in FIGURES 1 and 2, a spring 144- may be placed between a recessed pocket of cap S and the diaphragm plate 44, as shown. This spring may be utilized to balance the force of spring 78 as well as he weight of diaphragm assembly so that the pressures within chambers 34 and 48 may have a greater effect on the operational position of the diaphragm rather than be used to overcome the forces applied by the spring 7 8 and the Weight of the diaphragm and lever assemblies. This then makes the diaphragm 36 more sensitive to changes in both the air and the fuel pressures in chambers 34 and Thus the diaphragm is also more responsive to the required engine conditions determined at the nozzle 19@ and the low speed idle jet 116, as well as at the air ports 132, 133 and 127.

We claim:

l. A carburetor connected to the manifold of an internal combustion engine, said carburetor comprising a body, a fuel and air mixture conduit through said body, said body formed with a fuel chamber, said mixture conduit having an inlet and an outlet and a restricted portion intermediate said inlet and outlet and having a shirt portion, a fuel inlet and a fuel passage extending from said fuel inlet to said fuel chamber, an inlet valve in said fuel passage between said fuel inlet and said fuel chamber, said body having a fuel connection from said fuel chamber to said mixture conduit at said restricted portion, means for operating said inlet valve, said operating means including a diaphragm operatively connected to said inlet valve and sealed `at its periphery to said body across said fuel chamber to form a wall thereof, means forming a single closed air chamber enclosing the side of said diaphragm opposite to said fuel chamber, said body including a first air passage means connecting said mixture conduit inlet to said air chamber to provide air at substantially atmospheric pressure in said air chamber, a second air passage means connecting said skirt portion to said air chamber to modify the pressure of air in said air chamber in accordance with the pressure of air flowing through said skirt portion, and a third air passage means connecting said manifold to said air chamber to modify the pressure of air in said air chamber in accordance with the pressure within said manifold.

2. The invention of claim 1 including means in said third air passage for restricting air flow between said manifold and said air chamber.

3. A carburetor connected to the manifold of an internal combustion engine, said carburetor comprising a body, a fuel and air mixture conduit through said body, said body formed with a fuel chamber, said mixture conduit having an inlet and an outlet and a restricted portion intermediate said inlet and outlet and having a skirt portion, a fuel inlet passage extending to said fuel chamber, an inlet valve in said fuel inlet passage, a fuel nozzle at said restricted conduit portion, said body having a plurality of fuel conduits from said fuel chamber to said fuel nozzle, means for operating said inlet valve, said operating means including a diaphragm operatively connected to said inlet valve and sealed at its periphery to said body across said fuel chamber to form a wall thereof, means forming a single closed air chamber enclosing the side of said diaphragm opposite to said fuel chamber to move said diaphragm, said body including a first air passage means connecting said mixture conduit inlet to said air chamber to provide air at substantially atmospheric pressurerin said air chamber, a second air passage means connecting said skirt portion to said air chamber to modify the pressure of air in said air chamber in accordance with the pressure of air flowing through said skirt portion, and a third air passage means connecting said manifold to said first air passage means to modify the pressure of the air in said air chamber by the variations in air pressure within said manifold, and a tapered metering rod fixed to said diaphragm and having a free end extending through one of said plurality of fuel conduits to vary the flow of fuel therethrough in accordance with the position of said diaphragm, said free end of said metering rod being of substantially the same size as said one fuel conduit for preventing the dow of fuel through said 9 10 Y one conduit when said diaphragm is moved to a position 2,520,120 8/50 Bodine 261-69 X closing said inlet valve. 2,827,272 3/58 Phillips 261-41 2,841,372 7/58 Phillips 261-41 References Cited by the Examiner 3,065,957 11/62 Phillips 261--35 UNITED STATES PATENTS 5 3,085,791 4/63 Phillips 261-35 1,285,115 11/18 Gardner 261- 41 3086757 4/63 Smlt'h 26134 2,160,067 5/ 39 Gistucci et al 261-69 X FOREIGN PATENTS 2,173,281 9/ 39 Lichtenstein 261-69 470,646 g/37 Gre'at Britain 2,422,402 6/ 47 Gazda 55-220 2,447,791 8/48 Barfod 261 ..69 10 GEORGE D. MITCHELL, Primary Examiner. 2,511,213 6/50 Leslie.

HERBERT L. MARTIN, Examiner. 

1. A CARBURETOR CONNECTED TO THE MANIFOLD OF AN INTERNAL COMBUSTION ENGINE, SAID CARBURETOR COMPRISING A BODY, A FUEL AND AIR MIXTURE CONDUIT THROUGH SAID BODY, SAID BODY FORMED WITH A FUEL CHAMBER, SAID MIXTURE CONDUIT HAVING AN INLET AND AN OUTLET AND A RESTRICTED PORTION INTERMEDIATE SAID INLET AND OUTLET AND HAVING A SKIRT PORTION, A FUEL INLET AND A FUEL PASSAGE EXTENDING FROM SAID FUEL INLET TO SAID FUEL CHAMBER, AN INLET VALVE IN SAID FUEL PASSAGE BETWEEN SAID FUEL INLET AND SAID FUEL CHAMBER, SAID BODY HAVING A FUEL CONNECTION FROM SAID FUEL CHAMBER TO SAID MIXTURE CONDUIT AT SAID RESTRICTED PORTION, MEANS FOR OPERATING SAID INLET VALVE, SAID OPERATING MEANS INCLUDING A DIAPHRAGM OPERATIVELY CONNECTED TO SAID INLET VALVE AND SEALED AT ITS PERIPHERY TO SAID BODY ACROSS SAID FUEL CHAMBER TO FORM A WALL THEREOF, MEANS FORMING A SINGLE CLOSED AIR CHAMBER ENCLOSING THE SIDE OF SAID DIAPHRAGM OPPOSITE TO SAID FUEL CHAMBER, SAID BODY INCLUDING A FIRST AIR PASSAGE MEANS CONNECTING SAID MIXTURE CONDUIT INLET 